A solid laser, semiconductor laser and gas laser having a large output and a small size, which radiate an ultraviolet ray, visible light or infrared ray having a wavelength of 300 to 1,200 nm, have become easily available, and these lasers are very useful for recording light sources used in the direct plate-making based on digital signals, for example, from a computer. Various investigations on recording materials sensitive to such laser beams have been made. Typical examples thereof include first recording materials capable of being recorded with a infrared laser having a wavelength of not less than 760 nm, for example, positive-working recording materials as described in U.S. Pat. No. 4,708,925 and acid catalyst crosslinking type negative-working recording materials described in JP-A-8-276558 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), and secondly recording materials responsive to an ultraviolet ray or visible light laser having a wavelength of from 300 to 700 nm, for example, radical polymerization type negative-working recording materials as described in U.S. Pat. No. 2,850,445 and JP-B-44-20189 (the term “JP-B” as used herein means an “examined Japanese patent publication”). Although these materials have image-forming sensitivity sufficient for practical use, further improvement in sensitivity has been requested in order to extend the life of exposure light source or increase a number of printing plates produced per hour (improvement in productivity).
Ordinarily, a binder is added to a photosensitive layer used in the image-forming material and the binder has a function for increasing image strength, heat resistance of the layer or the like. For instance, it is described that in the case of using a binder containing a maleimido group in its side chain, the heat resistance of the cured layer obtained is increased due to excellent thermal stability of the maleimido group (see JP-A-2001-337454). It is described that in the case of using a polymer containing an ethylenically unsaturated bond in its side chain, photosensitive compositions capable of providing a cured layer having high strength are obtained because the binder is involved in the polymerization to form a layer having higher crosslink density (see JP-A-6-105353). It is described that in the case of using a binder containing a cyclic ether group and an ethylenically unsaturated bond in its side chain due to high hydrophilicity of the cyclic ether group, image-forming materials capable of providing a cured layer having a preferable developing property with an aqueous solution and high strength are obtained (see JP-A-2002-12607). It is described that in the case of using a binder obtained by copolymerization of a monomer wherein a methyl group in the methacryl group is substituted with a hetero atom, since compatibility with a radical polymerizable compound is improved, an amount of the radical polymerizable compound can be increased thereby obtaining photopolymerizable compositions having good preservation stability and providing a layer having high film strength (see JP-A-2002-107927). It is described that in the case of using a binder containing as an alkali-hydrolyzable group, a lactone group or an acid anhydride group in its side chain, since the developing property is increased by hydrolysis of the lactone ring, photopolymerizable compositions capable of forming a cured layer with high sensitivity and high resolution are obtained (see JP-A-2004-317652). In the lactone group or acid anhydride group described as the alkali-hydrolyzable group in JP-A-2004-317652, a few functional groups having a dipole moment of 3.8 debye or more are involved. However, these groups incidentally have the dipole moment of 3.8 debye or more and the technical concept relating to the functional group having a dipole moment of 3.8 debye or more is neither disclosed nor suggested in JP-A-2004-317652. It is described that in the case of using a polymer including a phenyl group substituted with a vinyl group in its side chain, since the phenyl groups substituted with a vinyl group are present as an aligned state in the layer, the polymerization reaction is apt to progress so that photosensitive compositions having high sensitivity and being free from latent image fading can be obtained, although the reason for this is not clear (see JP-A-2001-290271). It is described that in the case of using a binder containing a multipoint hydrogen bond-forming group, because of the presence of crosslink due to the hydrogen bond in addition to crosslink due to the radical polymerization, polymerizable compositions capable of providing a layer having high sensitivity and high strength are obtained (see JP-A-2005-300817). In the amido group described as the multipoint hydrogen bond-forming group in JP-A-2005-300817, a few functional groups having a dipole moment of 3.8 debye or more are involved. However, these groups incidentally have the dipole moment of 3.8 debye or more and the technical concept relating to the functional group having a dipole moment of 3.8 debye or more is neither disclosed nor suggested in JP-A-2005-300817. Moreover, in any of the patent documents there is no description as to the increase in radical polymerization reactivity of the radical polymerizable compound by means of these binders and the resulting improvements in both sensitivity and printing durability.
On the other hand, with respect to short wavelength light of not more than 300 nm or electron beam, radical polymerizable compositions are especially important for photoresist materials. In recent years, in integrated circuits, the degree of integration is more and more increased and in the production of a semiconductor substrate of VLSI or the like, fabrication of super-fine patterns composed of line width of finer than half micron has been required. In order to fulfill such requirements, the wavelength of light source used in an exposure apparatus in photolithography is more and more shortened and the use of a far ultraviolet ray or an excimer laser (for example, XeCl, KrF or ArF) has been investigated. Further, the formation of super-fine patterns by an electron beam has been investigated. Particularly, the electron beam is regarded as a promising light source for next-generation pattern forming technique.
In the photoresist materials, also, further increase in sensitivity has been requested in order to increase the productivity.
Further, with respect to hitherto known PS plates, a step of removing the non-image area by dissolution (development processing) is indispensable and a post-processing step, for example, washing the printing plate after the development processing with water, treatment of the printing plate after the development processing with a rinse solution containing a surfactant or treatment of the printing plate after the development processing with an oil-desensitizing solution containing gum arabic or a starch derivative, is also necessary. The point that such additional wet treatments are indispensable is a large subject of investigation in hitherto known PS plates. Even when the first half (image-forming process) of plate-making process is simplified by the above-described digital processing, the effects due to the simplification is still insufficient as long as the last half (development processing) is the troublesome wet treatment.
Particularly, the consideration for global environment has become a great concern throughout the field of industry in recent years. In view of the consideration for global environment, a treatment with a developer closer to a neutral range and a small amount of waste liquid are subjects of further investigations. Further, it is desirable that the wet type post-processing is simplified or changed to a dry processing.
From this viewpoint, as one method for eliminating the processing step, a method referred to as on-machine development wherein an exposed printing plate precursor is mounted on a cylinder of a printing machine and the non-image area of the printing plate precursor is removed by supplying dampening water and ink while rotating the cylinder is known. Specifically, according to the method, the printing plate precursor is exposed and mounted on a printing machine as it is to complete development processing in a conventional process of printing.
A lithographic printing plate precursor suitable for the on-machine development is required to have an image-forming layer soluble in dampening water or an ink solvent and a bright room handling property suitable for development on a printing machine placed in a bright room.
However, it is substantially impossible for hitherto known PS plates to fulfill such requirements.
In order to fulfill such requirements, a lithographic printing plate precursor having provided on a hydrophilic support an image-forming layer in which fine particles of thermoplastic hydrophobic polymer are dispersed in a hydrophilic binder polymer is proposed (see, for example, Japanese Patent 2,938,397). In the plate-making, the lithographic printing plate precursor is exposed to an infrared laser to agglomerate (fuse) the fine particles of thermoplastic hydrophobic polymer by heat generated by light-to-heat conversion thereby forming an image, and mounted on a cylinder of a printing machine to carry out on-machine development by supplying at least any one of dampening water and ink. Since the lithographic printing plate precursor has the sensitive zone in an infrared region, it has also the handling property in a bright room.
However, the image formed by the agglomeration (fusion) of the fine particles of thermoplastic hydrophobic polymer is insufficient in strength and has a problem of printing durability as a printing plate.
Lithographic printing plate precursors including microcapsules containing a polymerizable compound incorporated therein in stead of the thermoplastic fine particles are also proposed (see, for example, JP-A-2000-211262, JP-A-2001-277740, JP-A-2002-29162, JP-A-2002-46361, JP-A-2002-137562 and JP-A-2002-326470). In the lithographic printing plate precursors according to such a proposal, it is advantageous that the polymer image formed by a reaction of the polymerizable compound is excellent in the strength in comparison with the image formed by the fusion of the fine particles.
Also, since the polymerizable compound has high reactivity, many proposals of isolation of the polymerizable compound using microcapsules have been made. Further, it has been proposed to use a thermally degradable polymer in a shell of the microcapsule.
However, in the hitherto known lithographic printing plate precursors described in Japanese Patent 2,938,397, JP-A-2000-211262, JP-A-2001-277740, JP-A-2002-29162, JP-A-2002-46361, JP-A-2002-137562 and JP-A-2002-326470, the image formed by laser exposure is insufficient in the sensitivity and printing durability and further improvements are requested. Specifically, in such a lithographic printing plate precursor of a simple processing type, a photosensitive layer having high hydrophilicity is used in order to make development with an aqueous solution having pH of 10 or less or dampening water (ordinarily nearly neutral) on a printing machine and as a result, the image area is apt to be destroyed. Even when the binders as described in JP-A-2001-337454, JP-A-6-105353, JP-A-2002-12607, JP-A-2002-107927, JP-A-2004-317652, JP-A-2001-290271 and JP-A-2005-300817 are used in such lithographic printing plate precursors, lithographic printing plate precursors satisfying the simple processing aptitude, sensitivity and printing durability can not be obtained.